The effects of total parenteral nutrition (TPN) on the rapidly growing and developing gastrointestinal tract are unknown. This project will evaluate these neonatal acute and chronic TPN intestinal effects. We will also study separately the effects of partial enteral feeding and IV glutamine during TPN. The 3 day old piglet littermates will receive for 3 weeks either a balanced IV TPN solution containing amino acid (8 gm/kg/day), glucose (45 mg/kg/day), and fat (4.0 gm/kg/day), or an oral sow milk replacer (SMR) calorically equivalent to the TPN, or continue breast feeding. In Phase 2, after 3 weeks or TPN, the piglets will receive SMR for 2 more weeks and be compared to littermates who received SMR for 6 weeks. One of the 3 TPN littermates will receive glutamine (2%) as a portion of the TPN protein and another will receive 10% of his caloric requirement as SMR enterally. Phase B will extend the TPN period and recovery period to 4 weeks respectively and in 1 of 3 TPN animals, 25% of the total caloric requirement will be given as enteral SMR. Evaluations pre-study, after 3-4 weeks of therapy and pre- necropsy after 6-8 weeks of nutrition include: (1) Intestinal loop perfusion studies with an isotonic balanced salt solution containing sucrose, xylose, casein hydrolysate, and PEG; (2) Proximal and distal small intestinal biopsies at the above specified intervals and at necropsy for histology, disaccharidase levels, polyamine and diamine oxidase activity as well as serum diamine oxidase levels. At necropsy, gross morphology and anatomic measurements, intestinal protein, DNA content, and labeling indices will be measured. This study will define both the acute and chronic histologic, enzymatic and functional intestinal effects of neonatal TPN. It will describe the intestinal effects of giving either 10% or 25% of the TPN caloric needs as enteral feedings and determine if IV glutamine will prevent the deleterious intestinal effects of TPN.